Electroacoustical apparatus



Dec. 12, 1939. J..AND|-:RsoN

v ELECTROACOUSTICAL APPARATUS Filed Sept. 30, 1956 2 Sheets-Sheet 1 f y :inventor Leslie JHnderson (Ittomcg Dec- 12, 1939- l.. J. ANDERSON 2,183,209

ELEcTRoAcousTIcAL APPARATUS Filed sept. so, 195e .2 sheets-sheet 2 lll|IIIIHLIHIIIIIHIHIII IFI-2G43.

FREQUENCY /N CYCLES PEI? SECOND Bg Gttomeg 10000 nventor Patented Dec. 12, 1939 UNITED STATES ELEOTBOACOUSTICAL APPARATUS Leslie J. Anderson, Westmont, N.-J., assignor to Radio of Deia orporation of America, a corporation Application September 30, 1936, Serial No. 103,405

lclaims.

This inventionrelates to electroacoustical apparatus, and more particularly to a microphone of the velocity type such as that disclosed and claimed in the United States patent to Harry F.

Olson, No. 1,885,001.

When a velocity microphone of this type is placed close to a small sound source, the low frequency response is considerably accentuated. Since the mouth of a speaker or singer represents a relatively small source of sound, accentuation of low frequencies results when a velocity microphone is employed for close talking. To offset this effect, transformers for such micro-` phones have been designed so that they provide l5 a certain amount of low frequency attenuation.

However, when this is done, the resulting pickup of a plane wave or a near plane wave, such as that obtained from an orchestra, which represents a large sound source, will be lacking in low frequency response. 'Ihis has necessitated either using two different kinds of microphones where, for example, both orchestral music and voice-are being broadcast, one having a flat low frequency response and the other an attenuated low frequency response, or, if but a single microphone is used to pick up sound from both sources, a compromise between the two microphones was necessary with resulting loss in fidelity.

The primary object of my invention is to overcome the foregoing difliculty by the provisionl of an improved microphone of relatively high sensitivity and the response characteristic of which may be selectively controlled in such a manner as to best suit the particular purpose desired. More specifically, it is an object of my'invention to provide an improved microphone of the type set forth, the low frequency response of which may be readily and easily adjusted to obtain either a flat low frequency response oran attenuated lowv frequency response, depending upon whether the microphone is tobel used to pick up mainly music emanating from a relatively large source and at a relatively great distance therefrom, or whether it is to be used to pick up sound emanating from ones mouth in relatively close proximity thereto.

A further object of my invention is to provide an improved microphone as aforesaid which can be changed to provide one response characteristie or the other .without necessity ofdisassembling the same.

It is also an object of myinvention to provide an improved microphone of the type described which. is simple in construction, yet highly elvl5 cient in use.

(ci. 11a-r) In accordance with my invention, I provide a reactor which may be connected, at will, across at least a portion of the secondary of the output transformer of the microphone, the reactance thereof beingV of such a value that proper attenua- 5 tion is obtained at the low frequency end when such connection is made. When the reactor is renoved from across the transformer secondary, however, the microphone will have a substantially flat response. Preferably, although not nec'essarily, the reactor and the transformer may be housed in. a common shielding case and the reactor connected across the transformer secondary by means of a jumper to which access may be had readily through a small opening in the transl5 former casing. .Suitable indicia, visible through said opening, may be provided to indicate the operating condition of the microphone.

The novel features that I consider characteristic of my invention are setforth with particularity 'in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description of one embodiment thereof, when read in connection with the accompanying drawings in which- Figure 1A is a front elevation of my improved microphone-with the casing and wind screen removed,

Figure 2 is a circuit diagram showing the connections between the vibratible ribbon and the transformer, and showing, also, the manner of coupling the reactor to the transformer,

Figure 3 is a curve showing the difference in low frequency response of the microphone with the reactor coupled a-nd uncoupled from the transformer, and

Figure 4 is a circuit diagram showing a modification of my invention. 40

Referring more speciiically to the drawings, wherein similar reference characters designate corresponding parts throughout, there is shown, inY Fig. 1, a supporting yoke l which swivelly carries a pair of mounting pins 3 secured to a U- shaped, preferably non-magnetic-but electrically conductive bracket member 5. Secured to the upper ends of the arms 5a and ,5b of the bracket 5 are a pair of pole pieces 1 in spaced relation to each other to provide an air gap therebetween in which a conductive element 9, such as a thin, corrugated ribbon of aluminum, is mounted for vibratory movement. The conductive ribbon 9 has its upper end tightly clamped between a pair of blocks Il and I3,.the former of .which is of non- 55.

conductive material and the latter of which is of conductive material, the block being secured to the pole pieces 1, as by means of screws I5. The lower end of the conductive ribbon 9 is similarly tightly clamped between a second pair of blocks and |3 through'the latter of which extends a pair of set screws I1 locked thereto by the nuts I9. The set screws I1 are threaded into the lower ends of the pole pieces 1 and may be adjustably xed therein by means of the nuts 2 This construction permits adjusting the tension of the conductive ribbon 9 by manipulating the nuts I9 and the nuts 2| in the manner full?,7 set forth and claimed in my copending application Serial No. 88,174. A pair of magnets 23, one secured to the lower ends 0f the pole pieces 1 and the other to the upper ends of the pole pieces lower end of the conductive ribbon 9 is connected A to one side of the primary winding of the transformerby a lead 35, while the upper end of the conductive ribbon is connected to the arms 5a and 5b of the bracket member- 5-by means of a pair of leads 31 and 39, a lead 4| connecting substantially the midpoint 5c of the bracket member 5 with the other side of the primaryl winding of the transformer 29. This arrangement, which is particularly advantageous in pro- 'viding a pair of balancing loops which include the ribbon element 9 'for eliminating inductive pickup, is fully disclosed and claimed in my copending application Serial No; '77.142, now Patent No. 2,113,364, granted April 5, 1938.

Mounted within the casing member 21 isv a terminal board 43 of insulating material to which are fixed a plurality of conductive strips 45, 41, 49, 5|, 53 and 55. The transformer 29 is one which may have a frequency response characteristic tending to aid in the reproduction of a preponderance of base frequencies in the transmission of voice signals from the conductive element 9, and is preferably provided with a split secondary winding consisting of the coils 51 and 59. One side of th'e coil 51 may be connected to the strip 45 and the other side thereof to the strip 49, while the winding 59 may have one side connected to the strip 41 and its other side connected to the strip 5| and, by connecting a jumper or link 6| -across the strips 41 and 49,., the windings 51 and 59 are connected in series. In ac-` nected across at least a portion of the secondary winding of the transformer 29, one side of the reactor 33 being connected to the strip 53 -9 and the other side thereof being connected to the strip 5|, alead 95 connecting Ithe strip 41 with the strip 55.- Asecond jumper or link connection 31 is arranged to be connected, at will, across the strips 53 and 55 and, when so connected, couples the reactor 63 across'the winding 59 in parallel relation thereto. The. reactor 83 is so designed that, when itgis connected across the winding 59, it greatly reduces the output impedance of the transformer, thereby greatly atioI resents the preferred characteristic for a plane wave field emanating from a large sound source at some distance from the microphone. As will be observed from an examination of Fig. 3, there is a sharp decline at the low frequency end of the curve (designated Voice) when the jumper 61 is bridged across the strips 53 and 55, in which case. the reactor 63 is connected inparallel relation to the winding 59.

The jumper or link connection 61 may bepermanently pivotally secured to the strip 53, as by means of a bolt 69. Connection of the jumper 61 2to the terminal 55 may be readily effected by means of a screw 1| in the strip 55 which is received in the slot 13 of the jumper 61 when the jumper 61 is moved up into bridging relation, after which the screw 'il may be tightened against the jumper or link 61. The hole 33 is `formed to provide easy access to the screw 1| and the jumper 61. The terminal board 43 is preferably marked with the letter M and the jumper 61 with the letter V to indicate the 0perating condition of the microphone, the letters M and V. being readily visible through the opening 33 and representing, respectively, Music and Voice. Thus, the operator can tell at a glance throughi 'the opening 33 whether the microphone is set for voice transmission or for music transmission, and by merely -iinserting a screw driver through the opening 33, the screw 1i can be easily manipulated to permit either removal of the jumper 61 from bridging position to the open position shown in Fig. 2, or vice versa. The output from the microphone may be obtained by means of a cable represented by the leads 15 (Fig. 2) connected to the strips 45 and 5|.

Although I have shown and described but one modification of my invention, I am fully aware that many other modifications thereof and changes therein are possible without departing from the spirit thereof. For example, other means than that specifically shown in the accompanying drawings for connecting and disconnecting the reactor 63 across the coil 59 may be employed. Thus, a resistor, either fixed or variable (but shown as a variable resistor 11 in Fig.(4), may be substituted for the jumper 61, in which case varying degrees of attenuation represented by curves falling between the two curves shown in Figure 3 may be obtained. Also, if found desirable, the reactor 63 may be connected across both windings 514 and 59 instead of merely the winding 59. 'Furthermore instead of making the opening 33 in the cover plate 3| largeenough to' provide access to the screw 1| as well as to permit Vviewing of the letters M and V, thehole 33 may be made small. enough to permit only the viewing of the letters M and V. and access to the screw 1| made possible only by the-removal ofthe cover plate 3|. This hasA the advantage of preventing easy tampering with the screw 1| and therefore of perhaps avoiding misadjustment of the operating condition of the microphone by amazes nected to said element, acompensating reactor for attenuating said base frequencies, a terminal board, the secondary Winding of said transformer and said reactor each having leads connected to said terminal board, and means on said terminal board for connecting said reactor at will across at least a portion of said secondary winding for altering the response characteristic of said apparatus.

2. In a microphone having a predetermined response characteristic for sound energy in the range of speech tending to accentuate base frequencies when the sound source is relatively small and relatively close to the microphone, the combination of a vibratible conducting element mounted for movement in a magnetic field, an

output coupling transformer having its primary.

winding connected to said element, said transformer having a frequency response characteristie tending to aid in reproduction of a preponderance of base frequencies in voice transmission from said element, base frequency attenuating means adapted to cooperate with'the secondary winding of said transformer to provide a predetermined desired attenuation "of low frequency sounds in the voice range when connected in parallel relation to at least a portion of said secondary winding, a terminal board to which said secondary winding and said attenuating means are connected, and a movable link connection on said terminal board arranged to connect said attenuating means at will in parallel relation to said portion of said secondary winding.

, 3. The invention set forth in claim 2 characterized by the addition of a casing in which said transformer, said attenuating means and said terminal board are allA housed.

4. The invention set forth in claim 2 characterized by the addition of a casing in which said transformer, said attenuating means and said terminal board are all housed, said casing being provided with an opening through which said link connection may be adjusted to connect said attenuating means to and disconnect it from said secondary winding.

5. The invention set forth in claim 2 characterized by the addition of a casing in which said transformer, said -attenuating means and said terminal board are all housed, said casing being provided with an opening through which said link connection may be adjusted to connect said attenuating means to and disconnectit from said secondary winding, and characterized further by the addition of means for indicating the position of said link connection.

6. In a microphone having a predetermined response characteristic forsound energy in the range of speech tending to accentuate base frequencies when the sound source is relatively small and relatively close to the microphone and a wider, more generalrange for music emanating from a relatively large sound source at a relatively great distance therefrom, the combination of a vibratible conducting elementl mounted for movement in a magnetic field, an output coupling transformer having its primary windingconnected to said element, said transformer having a frequency response characteristic which tends to aid in reproduction of a preponderancel of base frequencies in voice transmission from said element, a terminal board having terminals connected lwith the secondary winding' of said transformer, additionalterminals on said terminal board having a movable link connection for selectively connecting said additional terminals to and disconnecting said additional terminals from each other, and a compensating reactor arranged to be connected across at least a portion of said secondary winding through said.

terminal board and said additional terminals and link connection.l

7. The invention set forth in claim 'I characterized in that said movable link connection consists of a resistor.

8. The invention set forth in claim "I characterized in that said movable link connection consists of va variable resistor.

9. The invention set forth4 in claim 7 characterized in that said compensating' reactor has a characteristic such that,4 when .said reactor is connected across said secondary winding portion, Y a predetermined attenuation of base frequencies in the voice range is obtained.

l0. The invention set forth in claim '7 characterized in that said secondary winding portion has leads connected with two terminals. on said terminal board, and characterized further in that said reactor has one lead connected with one of said terminals and its other lead connected to.

one of said additional terminals, the other of said additional terminals being connected to the other of said rst named terminals.

11, The invention set forth in claim 7 characterized by the addition of a casing in which said transformer, said reactor'aud said terminal board are all housed, said casing having an opening therein through which access may be had to said link connection for selectively bridging s aid additionalterminals whereby to connect said reactor across said secondary winding portion.

12. The invention set forth in claim 7 characterized by the addition of a casing in which said transformer, said reactor and said terminal board are al1 housed, said casing having an opening therein through which access may behad to said link connection for selectively bridging said additional terminals whereby to connect said reactor across said'secondary winding portion, and characterized further. by the addition of indicia on said terminal board and said link connection visib'.e through said opening for indicating the Patent No. 2,185,209.

CERTIFICATE oF' CORRECTION.

December l2, 1959.

LESLIE J. ANDERSON.

of the abeve nmnbered patentv requiring correction as follows: Page 5, second column, lines 27, 50, 55, 59, )4,8 and 56, claims 7, 8, 9, lO, ll and l2 respectively, for the 'claim reference numeral "7" read 6; and that the said Letters Patent should be read with this correction therein that the same may conforxp to'the record of the case in the Patent Office.

Signedend sealed this 6th dey Aof February, A. D.'19LLO.

Henry Van Arsdale,

(S931) Acting Commissioner of Patents.

It is hereby certified that error appears in the printed specification 

